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The
controlled stepwise dilatation technique is extremely important in order
to avoid creating severe mitral regurgitation during PTMC. Our balloon catheter
selection and balloon-sizing methods in the stepwise dilatation technique
have evolved from continuing efforts to minimize this complication [1-5]. BALLOON CATHETER SELECTION The catheter selection guidelines are based on the balloon RS derived from patient height, transthoracic echocardiographic findings of the mitral valve, and fluoroscopic presence of valvular calcification (Table I). Balloon Reference Size (RS) The RS is calculated according to this simple formula [1,4]: patient height (in cm) is rounded to the nearest zero and divided by 10, and 10 is added to the ratio to yield the RS (in mm); e.g., if height = 147 cm, then RS = 150/10 + 10 = 25 mm. Table 1. Reference Size and Catheter Selection  Height (cm) (rounded to the nearest 0) x 1/10 plus 10 e.g., height = 147 cm RS = 150 x 1/10 + 10 = 25 mm Catheter Selection Based on Patient Height/Valvular status
Calcified/SL Under-sized (One size < RS-matched; e.g., PTMC-24 for RS = 25 mm)
Catheter Selection In patients with pliable, noncalcified valves, as determined by echocardiography, a catheter with a nominal balloon size at least that of the RS (an RS-matched catheter) is used. In contrast, in patients at high risk for creating severe mitral regurgitation (valvular calcification [3] and/or severe subvalvular lesions [3, 6,7]), a balloon catheter one size smaller than an RS-match is selected. Therefore, in the above example with an RS of 25 mm, a PTMC-26 catheter would be selected for a pliable, noncalcified valve, and a PTMC-24 catheter for a calcified valve and/or a valve with severe subvalvular disease. STEPWISE DILATATION TECHNIQUE In order to avoid or minimize the complication of severe mitral regurgitation, the selection of an appropriate balloon catheter (discussed above) and adherence to the controlled stepwise dilatation technique are mandatory. Firstly, one should be familiar with the pressure-volume relationship and inflation limit of the less compliant balloon of the second-generation catheter now in use [2]. |
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Pressure-Volume Relationship (Fig. 1) The intra-balloon pressure transits from the "low-pressure" to the "high-pressure" zone as the balloon is inflated to within 2 mm of its nominal size, e.g., the 24-26 mm zone in a 26 mm-balloon catheter. Each catheter can be safely inflated to a maximal diameter of 1-2 mm above the nominal size because of the built-in safety margin. Initial balloon inflation is never to be performed with the balloon diameter in the high-pressure zone regardless of the valvular morphology. Balloon-Sizing (Table 2) Balloon sizing for the stepwise dilatation technique is crucial in avoiding the complication of severe mitral regurgitation. By adhering to the |
Figure
1 Reproduced by kind permission of Toray Industries, Inc. Click To View Larger Image |
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| cautionary
methods outlined below, especially in patients with severe subvalvular disease,
creation of significant mitral regurgitation (increase of > 2+ angiographically)
can be minimized [5]. I. Patients with pliable, non-calcified valves In patients with pliable, noncalcified valves and no severe subvalvular lesions, as determined by the subvalvular reassessment outlined above, an RS-matched balloon catheter is selected as stated previously. The initial inflated balloon diameter is RS minus 2 mm. In subsequent dilatations, the balloon size is increased by 1 mm. When there is preexisting mitral regurgitation or any question of increase in the degree of mitral regurgitation, the increment should be 0.5 mm in the high-pressure zone. This approach also applies when unilateral commissural splitting occurs during the previous dilatation, as observed by asymmetrical balloon waisting on fluoroscopy. The final balloon diameter is best kept within 1 mm above the RS to avoid oversizing: our previous study [1] showed that oversizing of the balloon is a risk factor for creating severe mitral regurgitation in this group of patients. |
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| Table
2. Balloon-Sizing in Stepwise Dilatations Valvular status Initial Increments I. Pliable |
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| MR
0/1+ MR 2+ II. Calcified/SL |
(RS
- 2) mm (RS - 4) mm (RS - 4) mm |
1
mm (low and high-low-pressure zone) 0.5 mm (high-pressure zone), if increase in MR, or unilateral commissural split 1 mm (low-pressure zone) 0.5 mm (high-pressure zone) 1 mm (low-pressure zone) |
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MR = mitral regurgitation, preexisting or increased; RS-matched = catheter with its nominal balloon size > RS; SL = severe subvalvular lesions; Low-pressure zone = balloon diameter < 2 mm of nominal balloon size; High-pressure zone = balloon diameter within 2 mm of nominal balloon size. |
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II. Patients with calcified valves and/or with severe subvalvular disease (Fig. 2) |
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In patients with either fluoroscopically visible valvular calcification, or severe subvalvular lesions as observed by transthoracic echocardiography, instead of an RS-match, a balloon catheter 1 size smaller than the RS-match is selected at the outset. For those whose subvalvular lesions are not detected by pre-procedural echocardiography, the RS-matched catheter alreadyplaced in the patient may still be used if the dilatation procedures are carried out with extra care. Ideally, the catheter should be exchanged for a smaller one, but this is quite costly. For the first dilatation, a balloon diameter 4 mm less than the RS is used. For subsequent |
Figure 2 Incremental reduction in mitral valve gradient with stepwise dilatations  Click To View Larger Image |
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| dilatations,
the balloon size is increased by 1 mm in the low-pressure zone and by 0.5
mm in the high-pressure zone until satisfactory results are obtained or
until mitral regurgitation develops. In cases where the gradient has already
been reduced to one-half and several more dilatation attempts have failed
to reduce it further, the procedure is terminated to avoid creating severe
mitral regurgitation [2]. Reducing the mitral valve gradient by one-half
should result in a 41% increase in the mitral valve area, as calculated
by the Gorlin formula, provided that heart rate and cardiac output remain
the same. Our previous study [2] suggests that a 40% improvement is sufficient
for symptomatic improvements in patients with a more sedentary lifestyle. References:
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© 2002-2003 Dr. Jui-Sung Hung. All Rights Reserved.
Questions or Comments? Email shung@pipeline.com. |
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